Field of the Invention
The present invention relates generally to ball valve seal assemblies and, more particularly, to a ball valve tertiary seal assembly.
Description of the Prior Art
Ball valves have been used for years and have employed closure members of a generally spherical shape. These members are rotated about one of its axes to align or place out of line the through-port with the flow passages of the body member to establish the open and closed positions of the stopper. The provision of the closure member in spherical form has a number inherent advantages, not the least of which is overall compactness of the valve and that it requires only one quarter turn of the closure member or spherical stopper to move from open to close and from close to open, as distinguished from the gate type valve where the stopper member must be shifted axially to and from closed position. As distinguished from the tapered or conical type of stopper, all difficulties of the “wedging” effect are avoided.
Ball valves generally provide for a single seal between the ball and the seat on both sides of the ball to provide. The problem of maintaining an effective seal in high pressure ball valves has long been recognized. Prior efforts to solve the problem of maintaining a satisfactory seal in ball valves are shown in Hulsey U.S. Pat. No. 3,504,885 and Grove U.S. Pat. No. 3,339,886 referenced above.
Independently operable dual seals have also been provided to address this problem. Exemplary U.S. Pat. Nos. 5,338,003, 5,320,327 and 54,942 to John Beson disclose high pressure ball valves having dual, independent seat to ball seals, the dual seal arrangement including a primary seal and a secondary seal, each operating independently, in proper sequence, each acting in the same direction, and each being pressure actuated, with provision for relieving excess fluid pressure.
Further, an independent tertiary ball valve seal has been utilized in the past but this prior art design requires that the upstream and downstream seal assemblies are different in shape. In this prior art tertiary seal design, the ball valve can be changed from a ball valve with identical primary and secondary seals on both sides of the closure member to a ball valve with primary and secondary seals on one side of the closure member with a tertiary seal on the opposite side of the ball valve. This design would still have one seal to close off flow in the opposite direction. Changing between the two modes of operation is made more difficult due to the requirement of different seal assemblies when the tertiary or third seal is desired.
It is an objective of the present invention to provide a long-lived multiple seal valve which can be operated with dual seals in either direction or can be changed to provide a tertiary seal without a requirement for different seats on opposite sides of the ball making the ball valve considerably less expensive to manufacture and less complicated to change.
Consequently, those of skill in the art will appreciate the present invention, which addresses the above problems and other significant problems uncovered by the inventor that are discussed hereinafter.